tox: Keeping going with docs

Sphinx 1.8 introduced [1] the '--keep-going' argument which, as its name
suggests, keeps the build running when it encounters non-fatal errors.
This is exceptionally useful in avoiding a continuous edit-build loop
when undertaking large doc reworks where multiple errors may be
introduced.

[1] https://github.com/sphinx-doc/sphinx/commit/e3483e9b045

Change-Id: I129ce91b6d25075306d92904e1bdaf0edf94d25d

doc/requirements.txt

@@ -1,8 +1,8 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7' # BSD
-sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2;python_version>='3.4' # BSD
+sphinx>=1.8.0,<2.0.0;python_version=='2.7' # BSD
+sphinx>=1.8.0,!=2.1.0;python_version>='3.4' # BSD
 reno>=2.5.0 # Apache-2.0
 openstackdocstheme>=1.30.0 # Apache-2.0
 sphinxcontrib-apidoc>=0.2.0  # BSD

lower-constraints.txt

@@ -100,7 +100,7 @@ Routes==2.3.1
 simplejson==3.5.1
 six==1.10.0
 snowballstemmer==1.2.1
-Sphinx==1.6.2
+Sphinx==1.8.0
 sphinxcontrib-websupport==1.0.1
 statsd==3.2.1
 stestr==2.0.0

tox.ini

@@ -46,7 +46,7 @@ deps =
 commands =
     rm -rf doc/html doc/build
     rm -rf doc/source/apidoc doc/source/api
-    sphinx-build -W -b html doc/source doc/build/html
+    sphinx-build -W --keep-going -b html doc/source doc/build/html
 
 [flake8]
 # H106: Don't put vim configuration in source files
@@ -62,7 +62,9 @@ deps =
     -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/doc/requirements.txt
-commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
+commands =
+  rm -rf releasenotes/build
+  sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
 [testenv:lower-constraints]
 basepython = python3